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Waterfall Illusion

This phenomenon was named after the observation of Robert Addams (1789 – 1875) in 1834. The scientist after having watched a waterfall for long minutes he glimpsed at the neighbouring cliffs and felt as if the cliffs started to move.

Vízesés illúzió

How to use?

Watch the rotating spiral for twenty seconds, then look at the picture of clouds! The clouds will start moving after a while as if they were moving towards you. The lines of the spiral have such an effect as if they were rotating inwards and when we look at the clouds they seem to move to the opposite direction, to outwards.

What happens?

It is still under debate how this optical illusion comes alive. Supposedly we sense the motion in a way that out brain compares the signs of the nerves that are responsible for the movements of different directions. If we look at a still images then these signs are in balance. But if we look at a one-directed or repeated motion for a longer time then the nerves, that sense the movement of the given direction, get exhausted sooner or later. This is when the nerves, that are responsible for the movements of different directions, get relatively more active and therefore our brain senses a motion of opposite direction.